The invention relates to a luminescence-optical indicator for determining the activity of alkali metal ions in a sample solution, the solution being at least in indirect contact with the indicator, and a sensor configuration with such an indicator.
Measuring the activity of alkali metal ions is of particular relevance in medical applications. The electrolytic equilibrium in blood, for instance, is essentially determined by sodium and potassium among others, while lithium plays a major role for the cerebral function.